Power plant control means



Dec.' 1s, 1945. E. MARTIN l2,391,322.

POWER PLANT CONTROL MEANS `ATTOFN EVY Dec. 18 1945. E. MARTIN 2,391,323

POWER PLANT CONTROLIMEANS 26WTITIHHHHH ATTO RN E Y i menudo. 1s, 194s Powrzn PLANT CONTROL' MEANS Erle Martin, West Hartford, Conn., assigner /to United Aircraft Corporation, East Hartfordi Conn., a coporation of Delaware Application February 9, 1942,- Serial No. 430,095

18 Claims.

This inventionl relates to improvements in power plant control means and has particular reference to an improved-control means for a power plant such as Vthe propulsive power plant of an aircraft including a controllable-pitch' propeller and a propeller driving engine.

An object of the invention resides in the pro- -vision of an improved power plant control operative to prevent overspeeding of the power plant and particularly overspeeding incident to changes in power plant operation.

A further object resides in the provision of an improved power plant control means of the character indicated which is responsive to powerl plant operating conditions. tending to result in excessive power plant speed and which is eilective to ,take anticipatory speed reducing action before the condition actually results in overspeeding of the power plant.

Other objects and advantages will be more particularly pointed out hereinafter or will become apparent as the description proceeds.

In the accompanying drawings, in which like reference numerals are used to designate similar parts throughout, there is illustrated in several slightly modified forms a suitable mechanical embodiment for the purpose of disclosing theinvention. The drawings, however, are for the purpose of illustration only and are not to be taken as limiting or restricting the invention since it will be apparent to those skilled in the art that various changes in the illustrated em-l bodiment may be resorted to without in any way exceeding th'e scope of the invention.

In the drawings, Fig. 1 is a diagrammatic sectional view through a power plant control constructed according to the invention.

l Fig. 2 is a diagrammatic sectional'view through a fragmentary portion of the power plant control shown in Fig. 1, showing a somewhat modified form of control means constructed according of the power plant. A contributing cause to this deficiency is that the conventional type centrifugalgovernor, without anticipatory devices, is incapable of correcting speed changes until after a definite speed change has occurred. Even after the governor has started to correct the speed, a definite, and sometimes excessive, time interval elapses before 'the propeller-gov-y ernor combination can be actuated suiilciently to correct the speed variation. As an example, a propeller of the controllable-type is susceptible to overspeeding when engine power is regained after a temporary interruption. If. for instance, the airplane is put into a stall with the throttle closed, the propeller will move to an extreme low pitch condition in an eiort` to keep the speed constant. If now the airplane is put into a dive, or the engine throttle is suddenly opened, or both of these conditions occurf the propeller in low pitch will accelerate rapidly.

The governor cannot act to check the increase in speed by increasing the pitch until the speed has reached the definite value for which the governor has been set. Moreover, after the governor has initiated the correction, a time interval occurs before the blade angle of the propeller can be increased sufficiently to check the speed. This time interval and the resulting overspeeding will, of course, depend upon the inherent rate of pitch change of the propellenbut it is probable that some dangerous overspeeding would result from a, maneuver suchas that described, regardless of h'ow fast, Within practical limits, the propeller can change its pitch. The above described maneuvers are mentioned only by way of example and it will be obvious to those skilled in the art that various other operating conditions may involve a tendency towards ex-l cessive power plant speed.

'It is among the objects of this invention to provide an improved power plant control which will be effective to prevent `such overspeeding of the power plant by taking an anticipatory action to increase the pitch of the `propeller 'blades a safe time interval before the pitch' increasing action of the governor is'begun. Such an improved power plant control has been illustrated in several slightly modified forms in the accompanying drawings to which reference may now be had for a detailed description of the construction and operation of the improved control apparatus.

Referring to the drawings in detail, the numeral l0 generally indicates a hydro-controllable aeronautical propeller supported and driven by an engine, generally indicated at I2. In the arrangement illustrated, the propeller is carried upon a. propeller shaft I4 supported by the yen- 20, driven from the shaft I4 by the gears 22, 24,`

26 and 28 controls the speed of the power plant by changing the pitch of the propeller blades.

The gear 28 is on a shaft 3'0 which carries at one end a pair of governor flyballs 32 and at the other end a fluid pressure pump 34. The flyballs 32 act on one end of a slidable tubular valve plunger 36 reciprocable and rotatable in a relatively lxed valve sleeve 38, the action of the flyballs being opposed by a governor Speeder spring 40 which bears at one end on the plunger 36 and at the opposite end on a movable piston abutment 42. The piston abutment 42 is carried in a cylindrical abutment 44 reciprocably mounted in a cylindrical extension 46 on the governor cap 48 and provided along one side thereof with rack teeth 50 engageable by the teeth of a pinion 52 rotatable by the manually movable lever or pulley 54 to change the speed setting of the governor. The force of the governor speeder spring acting on the cylindrical abutment is atleast partially counterbalanced by a compression spring 56 interposed between the closed end of theabutment 44 and the closed end of the cylindrical extension 46.

Fluid under pressure from the outlet of the pump 34 is led past a pressure relief valve 58,

rwhich regulates the pump outlet pressure to a predetermined value, to a iiuid pressure line 60 connected through the channel 62 with a port 64 in the valve sleeve 38. A iluid line 66 leads from a port 68 in the valve sleeve to one end of an operating cylinder 10 of a servo-motor, generally indicated at 12. Apiston 14 in the cylinder 10 is secured 'on a shaft 16 and urged in one direction by uid pressure from the channel 66 -and in the opposite direction by a, compression spring 18 contained in a cylindrical casing 80. The shaft 16 is connected through suitable means, as diagrammatically indicated 'by the link 82, the Aslip joint 84 having relatively rotatable parts, and the link 86, with the propeller I0, which may be any suitable controllable-pitch propeller, to vary the pitch angle of the propeller in accordance with the movements of the piston 14 of the servomotor.

For a more detailed description of a suitable propeller I0 and the control means therefor reference may be had to United States application Serial No. 422,252, led December 9,'1941, by Donald W. Perin and Nelson R. Richmond, for

Propeller control means, and assigned to the as-J signee of this invention.

The governor vis provided with a compensating mechanism for stabilizing its operation and pre-t venting overcorrection of the propeller pitch. This compensating mechanism includes a cylinder 88 on the servo-motor, tandem with the cylinder 10 and containing a reciprocable piston 90 mounted on an extension of the shaft 16, a compensating plunger 92 carrying a piston 94 and slidable in a cylindrical bore 96 and a pilot valve 98 reciprocable in the tubular governor controlled valve plunger 36 and connected to the plunger 92 by a lever |00 having a fixed pivotalV support at |02. One end of the cylinder 88 is connected through the fluid channel |04 with the end of the bore 96 containing the plunger 92 so that when the piston 90 is moved to the left as viewed in Fig. l the piston 94 will be raised against the force of the compression spring |06 and when the piston 90 moves tothe right the spring |06 will move the plunger 92 downwardly. This will cause the piston portion at the end of the pilot valve plunger 98 to follow the lower ports in the valve plunger 36 as this valve plunger is moved by the flyballs 32 and speeder spring 40, the action of the plunger 98 being to gradually restrict the connection between the governor operated valve and the servo-motor as the movement of the valve plunger 36 ceases, to slow the operation of the servo-motor as the propeller pitch approaches the angle corresponding to the change speed demand of the governor. Fluid from the space below the piston 94 may flow through the needle controlled bleed valve |08 to permit the plunger 98 to return to its neutral position at a predetermined rate after it has been displaced by movement of the piston 90.,

Another Way of expressing the action of this compensator would be to say that the plunger 98 determines the neutral position of the governor and movement of this neutral position really changes the speed setting of the governor. During pitch changing movements in which the propeller pitch is being increased, to reduce the engine speed because it is higher than the governor speed setting, the compensator piston 94 moves the plunger 98 and changes the neutral position of the governor to in effect increase the governor speed setting. This then means that after the propeller has begun to check the engine speed oil flow to the servo-motor 14 will `be cut off or reduced while the governor still has a neutral position higher than normal. As the oil ow to the piston 94 decreases, due to slower movement of the servo-motor 14, the bleed |08 allows the piston to slowly return to its normal setting thus returning the governor to its normal setting. If the pitch setting is not already enough to hold the speed down to the normal speed setting the additional oil will gradually be admitted to slowly increase the propeller pitch as the piston 94 and plunger 98 return to normal and' thus gradually approach the desired speed without overshooting.

The change speed gear unit I8 comprises a drive gear IIO onxthe engine vshaft I6, a driven gear |I2 on the propeller shaft I4, a plurality of planetary gears, two of which are indicated at II4 and II6, carried by a cage IIB concentrically supported on the shaft I4 and a double annular gear |20 fixed in the engine easing |22. The annular gear |20 has two sets of internal gear teethof different diameter and each planetary gear has three sets of gear teeth at least two sets of which are of different diameters. One set of gear teeth of each planetary gear is constantly in mesh with the driven gear I2. A second set is constantly in mesh with the drive gear ||0 and either one of two sets of gear teeth on the planetary gears may be alternatively engaged with a corresponding set of internal gear teeth in the ring gear |20 by longitudinal move- 4coupling between the shafts I6 and I4. The cage I I8 and planetary gears are moved in gear shifting directions by a fluid motor comprising a piston |24v secured to the cage I|8 and recipro# cable in a cylinder |24 to the end of the engine casing |22. The opposite ends oLthe cylinder |20 are connected by the conduits |28 and .|24 with a manually operable two-way valve |22 which'is also connected with the iiuid pressure line |24 and the drain line |34. When the valve |22 is in the position illustrated, the-right hand end of thefcylinder |24 is connectedwith the valve ismoved to its alternative position; shown 'in dotted lines, the left hand end of the cylinton abutment in a direction to compress the speeder spring until the piston abutment contacts the limit stop |58, thus compressing the speeder spring 4|| and setting the governor for a higher speed control. The variation in the load' ingonthespeederspringissodesignedthatthe diierence in the-two speed settingsof the govplanetary gears as long as an appreciable amount The governor is drivenirom and controls the 't speed of the propeller shaft I4 and as the engine speed must be kept within certain limits it is necessary that the control be such that the propeller may rotate at a higher speed when the gear I8 is in its high speed drive than when the gear is in its low speed drive and also that the propeller does not tend to overspeed when the gear Il is in itsneutral or uncoupled condition as it might if itwere permitted to windmill at -arelatively flat pitch angle. In order to accomplish this object the propeller is provided with a speed adjustment interconnected with the gear shifting motor so that the speed setting of the governor will be automatically changed as the gear is shifted.

A iluid line 138 leads to the interior of the cylinder |26 at a location such that, when the piston 24 is in the portion of the cylinder |26 corresponding to a low speed ratio of the 'gear Il or an uncoupled condition of the gear, the end of the iluid line |28 is connected with drain through a drain channel |40 in the piston |24 and, when the piston is in the portion of the cylinder |25 corresponding to a high speed driving connection through the gear- I8, the line |24 is connected with the pressure line |34 through'the conduit `|22 and the interior of the cylinder |25.

The conduit |34 leads into one end of a cylindrical bore |42 within which is a piston |44 'operatively connected with a valve plunger |48 and urged in a direction opposing the force of hydraulicuid under pressure in the line |38 ernor is the same as the diiierence between the two speed drives of the gear train I8 so that the engine may continue to operate at the same speed and the governor will maintain the propeller at a speed corresponding to the gear ratio o! the gear I8 in use at any particular time. This unloading of the governor speeder spring with a consequent tendency of the propeller to go to a high pitch slow speed condition also eliminates the tendency of the propeller to overspeed by windmilling with the gear i8 in its neutral or uncoupled condit on. v

For amore detailed' description of the change speed gear and governor control reference may be had to United States Patent N0..2,365,204, is-

sued December 19, 1944, by Erle Martin and Nelson R. Richmond, for Multi-speed governors. The present invention relates particularly to control apparatus operatively combined with the above-described control mechanism for preventing the propeller from overspeeding when the engine power is rapidly increased, as it would if the propeller were in a :dat pitch condition at the beginning of the engine .power increase and the power increased at a rateabove the corrective rate of they governor 2lil and propeller pitch changing motor. With this above described control apparatus, the propeller may still go to a nat pitch condition in its attempt to maintain the speed for which the governor is set if the engine power is reduced to a point at which the propeller speed falls below the governor speed setting. If the propeller were in such al flat pitch condition and the engine power were rapidly increased at a rate beyondvthe corrective rate of thel governor and pitch changing motor or i! the propeller speed suddenly increased as by windmilling in a dive, there would be serious danger of the propeller speed becoming dangerously high before the propeller pitch could be -adjusted to correct the overspeed condition. This is particularly true in the case of a governor of the character illustrated and described above since the governor does not begin its corrective action until a lpropeller speed corresponding to the particular governor speed setting has been exceeded. v

In the improved control arrangement the annular reaction gear |20 is mounted in the casing |22 in such a manner that it may have a limited freedom oi rotational movement in the casing. This movement of the gear |20 is resisted by an expansible chamber device or torque sensitive unit, generally-indicated at |58 and including a cylinderl |60 rigidly secured to the engine casing and a pistonf||2 operatively connected with the gear |20 by suitable means, such as the pistonrod |l4andthepivotalconnectioni. Fluid is interposed between the piston and the cled end |88 of the cylinder |88 and the pressure ot Y this iluid is indicative of the torque transmitted through the gear train |8 between the shafts I8 and I8. For a more complete description of a typical torque sensitive unit of the character indicated reference may be had to an article entitled Flight testing with an engine torque meter, by A. Lewis MacC'lain and Richard S. Buck, in the Society of Automotive Engineers Journal for February, 1938. Y

A iiuid line |10 leads from the fluid chamber in the torque responsive device |58 to a servo device having a cylinder |12 which reciprocably receives the small portion of a double piston |18 the larger portion of which is reciprocable in a cylinder |18 the end of which is connected through a fluid channel |18 with the channel |88 leading from the servo-motor cylinder 88 to the space in the bore 98 below the compensating plunger system 94. A spring |88 in the cylinder |16 urges the piston |18 against the force of uid under pressure in the line |10.

With this arrangement a decrease in engine torque will permit the piston |62 to rise in the cylinder |80 thereby relieving the pressure on piston |18 and permitting spring |88 to increase the space between the large end of the piston |18 and the closed end of the cylinder |18. This will remove fluid from below the compensator piston 94 and permit the plunger 92 to descend thereby raising the pilot valve 98, which will permit fluid to drain from the cylinder 10 of the servo-motor 'l2 through port 08 and the interior of tubular valve plunger 38 so that the servoinotor will move under the influence of the spring 18 in a direction to decrease the propeller pitch If the engine torque is increased, however, this process is immediately reversed and the pilot valve 98 will be lowered in thefvalve plunger 38 thereby connecting the cylinder I0 of the servomotor withthe pressure line 60 and causing the servo-motor to move, in a direction to increase the propeller pitch. As the mechanism including the torque sensitive device |58 and the pls-5 ton |18 acts as soon as there is an increase inV engine torque and before there is a material increase in propeller speed, the propeller pitch will start to increase long before the propeller speed reaches the value at which the governor is set and the rate of increase of propeller speed is retarded to such an extent that the governor can easily take care of the speed increase as the propeller speed approaches and passes the governor speed setting. By permitting the propeller pitch to decrease as the torque decreases, this control device does not interfere with the governor control for the change speed gear and both controls will eiectively perform their function in the same combination without mutual interference.

The arrangement shown in Fig. 3 is substantially the same as that shown in Fig. 1 except that the fixed pivotal support |02 of the lever |00 in Fig. 1 is replaced by a movable support |8| carried at one end of a lever |82 having a pivotal support at |84 and pivotally connected at its end opposite the pivotal support |8| with the rod |86 of a piston |88 reciprocable in a cylinder |90 between the limit stops |92 and |98.

Fluid pressure from the torque sensitive device |58 is supplied to one end of the cylinder |90 of a'servo device |9| through the fluid line |10 to move the piston |88 against the force of the compression spring |96 located in the oppo-'o site end of the cylinder |90.

'iluid line |18 decreases.

the piston |88 against the stop |92 raising the asonsas With this arrangement an increase in engine or propeller torque will force uid through the line |18 and move the piston |88 towards the limit stop |88 compressing the spring |88. This movement of the piston |88 will move the lever |82 about its pivot |88 raising the pivot support |8| of the leverA |88 and thus raising the pilot -valve plunger 88.

: ing normal operation, which is the condition shown in the drawings, lever |82 forms s xed pivot support for the lever |88 and centers the pilot valve plunger 98 in the lower port in the tubular valve plunger 38 when the yballs 32 are substantially parallel to the axis of the shaft 38 and the governor is in its on-speed" condition.

When a loss of'torqueroccurs, pressure in the Spn'i`g198-then forces lever |82 and lowering the pivot |8|. Lever |00 turning on its pivotal lconnection with the end of the plunger 92 as a pivot lowers the pilot valve plunger 90. At the same time the propeller slows down causing the ilyballs 82 to move inward and lower the tubular valve plunger 38. the pilot valve plunger 98 and the tubular valve sleeve 38 move downward at the same speed, the ports between them will not open and the propeller will not change pitch. Stop |92 is so adjusted that when the ilyballs 32 have moved inward to the limit of their travel, the pilot valve plunger 98 will have moved downwardly exactly as far as the tubular valve plunger 36, causing the governor ports to remain closed as long as the torque is oil. The total eiIect for short interruptions of torque is to lock the propeller in whatever pitch it is in when an interruption of power occurs; however, the locking is only effective in preventing the propeller from going to a lower pitch. If the propeller should tend to speed up due to windmill eil'ect or other cause, the pitch will increase to prevent speeding up but, should the propeller tend to slow down, the

Vpitch will not decrease because the governor ports cannot open to drain. Thus an overspeed limit is set up on the loss of engine torque and the speed to which the propeller is limited is lower than thel set speed of the governor by the amount of speed changes caused by moving the pilot valve plunger a distance corresponding to the inward limit of yball travel. This will depend on the speeder spring-flyball rate ratio.

'I'he effect of this limit control on gear shifting mechanism would be to cause the shifting of the gears to take place at a somewhat lower speed than in the combination shown in Fig. 1.

When the torque is re-established after an in# terruption the pilot valve is returned to its normal position and the governor set back to its normal speed which, 'as pointed out above, is higher than its limit speed. II the pilot valve .return is instantaneous or'faster than the engine increases in speed the propeller ports will be opened to decrease the propeller pitch. Under some conditions this might result in some overspeeding of the propeller but this could be prevented by suitable retarding means such as by making the lower end of the piston |88 a dash pot which would allow the piston to move upward instantaneously but move downward slowly with an increase oi engine torque.

Thus, if

A:aanwas I'he arrangement shown in Fig. 4 is also similar to that shown in Fig. 1 with the exception that the compensator pilot valve is not utilized to change the governor speed setting and to control the servo-motor but instead a change in the speedsetting of the governor by changing the speeder spring setting only is depended upon to accomplish this purpose. In this arrangementan additional piston |98 is interposed between the piston abutment 42 and the adjustable cylindrical abutment 44. The gear shift control line |50 is led to the space between the piston abutment 42 and the closed end of the hollow intermediate piston |98 and the torque meter pressure line is led to the space between the-in Atermediate'piston |98 and the closed end of the manually adjustable cylindrical abutment 44.

With this arrangement, when' the engine lis operating under power, or torque is otherwise being transmitted between the shafts I4 and I6,

the intermediate piston |98 will be held in posi- 1 tion with its lower end'against the' stop |56 of l the, outer cylindrical abutment, as illustrated in the drawings, and the position of the inner piston 42 relative to this intermediate piston willy be controlled by the gear shift motor in the manner explained a-bove. This position cf the piston |98 against the stop |56 will provide a minimum low speed setting for the governor while the engine is operating in gearand transmittingsubstantial torque to the propeller. When there is a loss of torque and consequent loss of pressure in the iluid line |10 the piston |98 will ris" in the cylinder .44 relieving the loading on the governor Speeder spring 40 and resetting the governor to a ,lower speed setting. If now the torque is re-established, the governcrs-will be initially set for a lower speed and will thus begin to correct for the increasing speed by increasing the propeller pitch angle before such correction would have been initiated with the governor in its normal speed setting. It is necessary that the application of pressure through the line |10 to the piston |98 lag somewhat behind the increasing speed of the propeller as the torque increases and to this end it may be found desirable to include a'- restriction in the line |10 or some other part of this portion of this hydraulic system.

In the arrangement shown in Fig. 2 the operation is the same as that of the device shownin F'ig.A 1 with the exception that a manifold torque pressure responsive element 200 is substituted for the hydraulic device |58 directly responsive to engine shaft torque, The device 200 may comprise an expansible chamber device in the form of a bellows or Sylphon interiorly connectedg with the engine intake system by a uid conduit 202. The upper end of the bellows 200 is; held in xed position by a suitable bracket 204 and the movable lower end carries a valve stem 206 which projects into a relay or servo v alve generally indicated at 208. This relay valve comprises two tandem cylinders 2|0 and 2`|2 separated by a diaphragm 2|4 and containing a plunger generally indicated at 2|6 having a piston 2|8 in the cylinder 2|0 and a piston 220 in the cylinder 2|2. 'I'he valve plunger 206 is reciprocable in a bore in the piston plunger 2|6 and acts to control the fluid valves 222 and 226. A

-pressure uid line 228 leads from the line 60 to the upper end of `the cylinder 2|0 and-a drain port 230I leads from the upper end of the cylinder 2|2l above the piston 220. An extensionr 232 on the piston plunger 2|6 extending through the the eiective area on the lower side of this piston being greater than the effective area on the .upper side thereof. The valve 222 controls the flow of uid under pressure from the line 228 and through the channels 223 and 224 to the space below the piston 2|8 while the valve 228 controls the flow of iiuid through the channels 224 and 221 from the space below the piston 2|8 to the exhaust port 230.

With this arrangement when a loss of torque occurs as evidenced by a lossofmanifold pressure the valve plunger 206 will rise admitting hydraulic fluid from the pressure line 228 to the underside of the piston 2|8 causing the piston plunger 2|6 to rise and the compensating plunger 92 to descend thereby raising the pilot valve plunger 98 maintaining the governor valve drain ports closed and preventing the propeller from going to a flat pitch condition in the manner explained in connection with the description of Fig. 1; When the torque again increases as evidencedby an increase in manifold pressure, the valve plunger 206 willgbe forced downwardly connecting channels 224 and 226 with the drainport 230 thus permitting the piston plunger 2| 6 to descend under the fluid pressure admitted through the line 228. 'I'he piston plunger 2|6 will descend until it reaches a limiting position with the piston 220 against the lower end ofthe cylinder 2 l2 and the plunger 98 will reassume its normal or neutral position under the inue'nce of the spring |48, The relay valve 208 is provided in order to provide a definite force acting on the` compensating plunger 92 and to prevent movements of the piston 90 in the cylinder 88 from moving the piston controlled by the manifold pressure responsive element 200.

Whil a suitable mechanical embodiment in several modified forms has been hereinabove described and illustrated in the accompanying drawings, for the purpose of disclosing the invention, it is to be understood that the invention is not limited to the particular embodiment so illustrated and described, but that such changes in the' size, shape and arrangement of the various parts thereof may be resorted to as come within the scope of the subjoined. claims.

Having now described the invention so that others skilled in the art may clearly understand the same, what it is desiredto secure by Letters sive means operati-velyconnected with said speed setting means to determine the position of s'aid setting means, said speed setting means being.

movable through its entire range by a torque change less than said torque range and said speed Setting means and said torque responsive means constructed and arranged to maintain said setting means at its high speed position for all torque values above a predetermined amount in maintain said setting means at its low speed pothe upper portion of said torque range and to sitionfor all torque values below a predetermined amount in the lower portion oi said torque. range. I

2. In combination with an engine, an engine driven variableload device, and a governor havof said range. i

ing means for selecting the speed to be maintained and operative to maintain the speed of said engine substantially constant at said selected speed by varying the load imposed on said engine by said variable load device, said governor requiring a time interval for varying said load proportional to the required amount oi load change, means for preventing overspeeding of said engine by an increase of torque at a rate greater than the load increasing capacity of said speed responsive means, `said overspeed preventing means comprising, mechanism responsive to engine torque variation within a predetermined range, and means actuated by said torque responsive mechanism to provide an acceleration resisting load in advance of the attainment of said selected engine speed,

3. In combination with an aircraft power plant including a controllable-pitch propeller, a propeller driving engine developing a predetermined range of torque values and speed responsive means regulating the pitch oi.' said propeller to control the speed o! said power plant to maintain a substantially constant preselected speed independently of torque values, means responsive to variations -in the torque of said engine, and means actuated by said torque responsive means and operatively connected with said speed responsive means to reset said speed responsive means for a lower speed setting when said torque ,decreases below a predetermined value in the lower portion 4. In combination withl an aircraft power plant including a controllable-pitch propeller, a prol peller driving engine and speed responsive means regulating the pitch of said propeller to maintain the speed of said power plant at a selected speed. said means having a lower pitch regulating limit at which the speed responsive means is rendered ineffective to reduce the propeller pitch, means responsive to variations in engine torque, and means actuated by. said torque responsive means and operatively connected with said speed responsive means to setsaid speed responsive .means at its lower limit to thereby restrain the pitch of said propeller from changing below a predetermined pitch angle when the engine torque decreases to' a value below that necessary to rotate the propeller at said selected speed.

5. In combination with an aircraft power plant including a controllable-pitch propeller, a propeller driving engine and speed'responsive means regulating the pitch of said propeller to control the speed of said power plant, a variable volume device responsive to variations in engine torque, means having a limited travel for resetting said speed responsive device, means limiting the travel of said resetting device, said variable volume device and said resetting means being operably connected and including means for moving said resetting means to one of its limiting positions to provide a low speed setting for said speed responsive device whenever the engine torque decreases below a predetermined value.

6. In combination with a power plant includv ing a controllable-pitch propeller, a propeller driving engine, and a speed governor driven by said power plant and including a propeller pitch controlling valve and a cut-o valve i'or said pitch controlling valve, an expansible chamber device responsive to variations in engine torque, and means operatively connecting said expansible chamber device with said cut-oil valve to hold said cut-off valve in position to restrain said propeller against pitch decrease whenever said engine therebyI maintain the speed of said torque is below a predetermined value.

7. In combination with a, power plant including a controllable-pitch propeller, a propeller driving engine, and a speed governor driven by said power plant and including a propeller pitch controlling valve and a cut-off valve for said pitch controlling valve, an expansible chamber device responsive to variations in engine torque, and means operatively connecting said expansible chamber device with said cut-o valve to move said cut-oil? valve to a pitch increasing position upon an increase in engine torque. Y

8. In a power plant including an engine, an engine driven controllable-pitch propeller and a speed governor operatively connected with said propeller to regulate the propeller pitch and power plant substantially constant at a selected value, said governor having a speeder spring, a piston bearing upon said spring, a variable volume device having an element m/ovable in response to -engine torque variations hydraulically connected with said piston for moving said piston a predetermined limit amount and increasing the load on said spring whenever said engine torque exceeds a predetermined value said piston ,reaching its limit of movement when the engine torque reaches a predetermined higher value less than the maximum torque of the engine.

9. In a power plant a range of torque values, anengine driven controllable-pitch propeller, and a speed governor oppitch, of said propeller, said governor having a Gil Speeder spring and a set of centrifugal flyballs acting against said spring, a ilrst variable volume device having a movable element operatively associated with said spring to change the loading thereon, stops for limiting the movement of said movable element, a second variable volume device,

responsive to variations in engine torque, and a hydraulic connection between said rst and slecond variable volume devices for transmitting nuid from one device to the other for moving said movable element from one stop to the other stop and increasing the loading on said spring upon a predetermined limited increase in engine torque in the lower portion of said range of torque values.

10; In a. powerplant including an engine for delivering a predetermined range of torque values, an engine driven Vcontrollable-pitch propeller, and a speed governor operatively connected with said propeller to maintain the speed of saidpower plant substantially constant at a selected value .by regulating the pitch of said propeller, means operatively associated with said governor and movableto different positions to vary the speed setting of said governor, hydraulic means operatively connected with said iirst mentioned means to change the position thereonxhydraulic means operatively associated with said engine to apply to hydraulic fluid Va pressure varying' in proportion to variations in engine torque, and a hydraulic connection between said two hydraulic means to render said ilrst mentioned hydraulic means effective to change the speed Vsetting of said governor when said engine torque reaches substantially a predetermined value in said range, said first mentionedA hydraulic means being ineffective to change the speed setting of said governor upon .changes in torque values in said range above and below said predetermined value.

including an engine having f assises movable element to hold said element stationary and to move said velement and change the speed setting of said governor, a hydraulic device operativelyassociated with said engine effective to apply to hydraulic iluid a pressure variable Iin proportion to variations in engine torque, a servo device hydraulically connected with said engine associated device and operated thereby, and an operative connection between said servo device and said ilrst mentioned hydraulic device torender said ilrst mentioned hydraulic device operative to temporarily change the speed setting of said governor.

12. In a powerplant including an engine, an

engine driven hydro-controllable propeller, a'

valve for controlling the flow of hydraulic fluid to and from said propeller, a speed governor con-r trolling said valve to maintain the speed of said power plant substantially constant at a predetermined rate, a, movable valve element operative to.

change the speed settingof said governor, and a hydraulic device operatively connected with said movable valve element for holding said element stationary and for moving the same, a hydraulic device operatively associated with said engine eii'ective to apply to hydraulic fluid a pressure variable in proportion to vvariations in engine selecting the speed to be maintained, for maintaining a preselected engine speed at different torque values by regulating the propeller pitch,

means for preventing overspeeding of said vengine upon a-sudden increase in torque from a torque value below a predetermined amount in the lower portion of said torque range comprising additional governor speed setting means having a limited range dened by a high speed position and a low speed position, said governor maintaining said preselected speed' when said setting means is in its high speed position, engine torque responsive means operatively connected with said speed setting means to determine the position of said setting means, said speed setting means being movable through its entire range by a torque f change less than said torque range, and said torque, a, servo device hydraulically connected with said-engine associated device-and operated thereby, and an operative connection between said servo device and said first mentioned hydraulic device to render said first mentioned hydraulic device and the movable valve element operatively associated therewith eiective to cut oi said controlling valve and thus .prevent a further decrease of propeller pitch after said engine torque has decreased to a predetermined value.

13. In a power plant including an engine, an engine driven hydro-controllable propeller, a valve for controlling the flow of hydraulic fluid to and from said propeller, a speed governor controlling said valve to maintain the speed of said power plant substantially constant at a predetermined rate, a movable valve element operative to change the speed setting of said governor, and a hydraulic device operatively connected with said movable valve element for holding said element stationary and for moving the same, a hydraulic device operatively associated with saidengine effective to apply to hydraulic iluid a pressure variable in proportion to variations in engine torque, a servo device hydraulically connectedwith said engine associated device and operated .thereby, and an operative connection between said servo device and said first mentioned hydraulic device to render said first mentioned hydraulic device and the movable valve element operatively associated therewith eiiective to open said controlling valve and initiate a pitch increase when said engine torque increases and before the speed of said power plant has varied from said predetermined rate.

14. In combination`with an aircraft power plant including a controllable pitch propeller, an engine having a predetermined range of torque values, and a speed. governor, having means for speed setting-means and said torque responsive means. constructed and arranged to maintain and operative to maintain'the speed of said en,.

gine substantially constant at said selected speed' at different torque values, said governor requiring a time interval *for varying said propeller pitch dependent upon the required amount of pitch change, means for preventing overspeeding of said engine by an increase of torque at a rate greater than the load increasing capacity of said governor, said overspeed preventing means comprising mechanism responsive to engine torque variations within a predetermined range-and means actuated by said torque responsive mechanism to initiate a change in propeller pitch to provide an acceleration resisting load. Y

16. In combination with an aircraft power plant including a controllable pitch propeller, and an engine having a range Aoi? torque values, a speed governor including governor controlled valve means controllingA the engine speed by regulating the propeller pitch, said governor having means for selecting the speed to -be maintained and operative to maintain the speed .of said engine substantially constant at said selected speed at diierent torque values, said governor requiring a time interval for varying said propeller pitch dependent upon the required amount of pitch change, means for preventing overspeeding of said engine by an increase of torque at a rate greaterthan the load increasing capacity of said governor, said overspeed preventing means comprising mechanism responsive to engine'torque variations within a predetermined range and means actuated by said torque"responsive mechanism to move said governor controlled valve means and provide a change in propeller pitch to vprovide an acceleration resisting load before substanti'al movement ofv said valve Ameans by saidl governor. ff

1'1t The combination with an aircraft power plant including a controllable pitch propeller, an engine, and a speed governor, including governor controlled valve means, for controllingthe engine speed by regulating the propeller pitch.

said governor having means for selecting the speed to be maintained by said engine and'operative to maintain the speed of said engine substantially constant at said selected speed at different torque values, of torque responsive means actuated byL a change in torque of said engine, means operatively connecting said torque responsive means and said valve means to render said valve means responsive to said engine torque and thereby position said propeller blades controlled by said valve means to anticipate/che effect 'of an increase in torque of said engine and prevent the engine from substantially exceeding said selected speed. 

